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Before the start of the heat wave, two derecho events took place; one on July 11 over most of the central Plains, the lower Great Lakes and the Appalachian region; the other on July 17 over eastern Ontario, southern Quebec and northern New England. On July 21, 2011, hot weather over the past week culminated into record-breaking temperatures across the province of Ontario, also in Michigan, Ohio, upstate New York and Quebec, shattering long held records.[2] Toronto reached 38 °C (100 °F) for the first time in nearly 10 years. The humidex reached 51 at the downtown station by late afternoon. It was deemed so hot that the unusual decision was made to close the dome at the Rogers Centre during the Toronto Blue Jays baseball game, usually done in the event of cold weather or rain.

The intense heat moved eastwards and peaked along the US I-95 corridor on July 22, 2011, with Central Park in New York City breaking the record for the day at 104 °F (40 °C) or more in the interior of city which was the hottest temperature the city had experienced in over three decades. Newark, New Jersey also reached an all-time record high of 108 °F (42 °C), as did Washington Dulles International Airport in Virginia at 105 °F (41 °C). Philadelphia surpassed its daily record when it reached 103 °F (39 °C), and Boston tied for the second highest temperature on record at 103 °F (39 °C), making it the hottest day in 85 years. The heat was blamed for at least 25 deaths across the Midwest and the Northeast.[3] Daily high temperatures warmer than normal began on the southern plains during May 2011, accompanied by one of the most severe droughts ever recorded.[4] The heat wave continued to intensify, with temperatures in north Texas exceeding 100 °F (38 °C) most days beginning in mid-June.

By July 27, the heat had intensified over the central plains, in Hutchison and Salina, Kansas temperatures reached 113 °F (45 °C).

In Oklahoma, by August 3, several locations in the southwestern portion of the state had recorded 43 consecutive days exceeding 100 °F (38 °C). Air temperatures exclusive of heat index exceeded 110 °F (43 °C) for much of the state on August 2 and 3, reaching 115 °F (46 °C) in Poteau and Wilburton on August 3. On the same day, Little Rock, Arkansas plateaued at 114 °F (46 °C) in the shade.[5]

As of August 10, Dallas/Fort Worth had recorded 40 consecutive days with high temperatures exceeding 100 °F (38 °C), the second-longest streak on record (the record of 42 days was set during the 1980 United States heat wave). In addition, the area set a new all-time hottest minimum temperature of 86 °F (30 °C) on July 26[6] and tied it twice in August. However by September 13, Dallas had endured 71 non-consecutive days with temperatures exceeding 100 °F (38 °C), beating the record of 69 days set in 1980.[7]

On August 24, a 5-hour long severe thunderstorm hit Southern Ontario that evening which also spawned a pair of weak tornadoes, nothing particularly unusual for August, but it set records for lightning frequency, thought to be fueled by abnormally high Lake Ontario water surface temperatures due to the heat wave.

The National Climatic Data Center in Asheville, North Carolina reported that the United States had the hottest summer on record in 2011. Since 1901, only the Dust Bowl era summer of 1936 was hotter. Texas, Oklahoma, New Mexico and Louisiana all reported their hottest summer on record. Based on an index of residential energy demand, 2011 was the hottest summer on record. However, the states of Oregon and Washington recorded cooler than average summers, while California recorded its wettest.[1]

The continuing heat and drought resulted in several lakes dropping to record lows, particularly in Texas and Oklahoma. This resulted in re-exposing old towns and other historical sites that were submerged by dam construction. The original site of Bluffton, Texas was re-exposed, revealing a town site that had been submerged under Lake Buchanan since a dam was completed in 1939. The town of Woodville, Oklahoma was also re-exposed as Lake Texoma dropped.[8]

In Colorado Springs, temperatures reached 97F (near record highs) as early as June. Daytime highs in June, July, and August were about 6F above average. Temperatures were elevated during the heat wave, but remained cooler than temperatures in the Great Plains to the east.

Denver, Colorado saw temperatures as high as 104F as early as June 19, 2011. Denver International Airport recorded a high of 102F on June 29, 2011. This broke the record of 95F set back in 1978. The high of 104F was set on July 28, 2011. This temperature broke the previous record of 100F set back in 1991.

Fully subjected to the heat wave, Wichita had an unusually hot summer in 2011. Wichita reached a temperature of 111F twice over the course of the heat wave, once in July, and once in August. Daytime highs in the months of June, July, and August averaged almost 9F over prior observed normals. The year was also substantially drier than average.

Oklahoma City, Oklahoma experienced extremely hot temperatures in the summer of 2011, and below normal rainfall. While winter, spring, and fall temperatures were close to normals, Central Oklahoma started to experience abnormally high temperatures after a very wet month of May. High temperatures in the months of June, July, and August were 9F above normals, and overnight lows were also significantly above norm. The heat was so extreme, that OGE, the area's main electricity provider, refused to cut off electric service in the month of August, as it felt that this might result in deaths among the elderly, many of whom used electric power to air-condition their homes.[11] The following data is for the weather station at Will Rogers World Airport, located southwest of the city, which during the summer, experienced a peak temperature of 110F. Due to the urban heat island effect, most of the urban area of Oklahoma City was even hotter than the temperatures recorded at the airport. One weather station, located in an urban part of the city, recorded an air temperature of 116F on August 3.[12] The heat wave finally ended on September 15, 2011, when a cold front moved though Central Oklahoma.

Lawton, Oklahoma experienced even hotter weather than Oklahoma City reported. In Lawton, daytime high temperatures during the months of June, July, and August averaged 11F above the previously observed normals, and nighttime lows averaged 8F above normal. In at least one weather station in Lawton, less than half the normal rainfall was recorded over the course of the year, and almost none was recorded during the summer.

Tulsa, Oklahoma was also affected by the heat wave with temperatures maxing out 113F on August 5, 2011. Temperatures of 111F was recorded in Tulsa on August 6, 2011. On August 8, 2011 temperatures maxed out 110F, almost breaking the 111F record set back in 1935. Up until October temperatures in Tulsa remained in the high 80s to the low 100s.

Dallas, Texas was affected by the heat wave. In Dallas, temperatures in the months of June, July, and August averaged 8 °F above normals. Dallas also received a below normal amount of precipitation during the year.

The Amarillo, Texas area, along with the rest of Texas and the Southern Plains, experienced the worst of the heat wave. Summertime temperatures soared at high as 111F in June, and the overall precipitation was only a third of the average. For the months of June, July, and August, average highs were 10F above normal, and overnight low temperatures were 6F above normal.